Example 2 Residual Stresses in Shot Peening

Shot peening is a cold working process in which thousands of spherical shot (typically '2 mm diam spheres of steel, glass, or ceramic) are propelled against the surface of a part. The overlap of the small craters formed by the impact of each sphere creates a compressive layer at the surface of the part. In this process, the intensity of the stresses generated typically exceeds half the yield strength of the material being peened. The depth of the residual stress layer obtained depends on the operating parameters of the process, including the intensity of the process as measured by Almen gages; the size, velocity, and impingement angle of the shot (Ref 41); and the characteristics of the material being shot peened.

Table 2 indicates the wide variation in fatigue life performance that can be obtained by varying the finishing process. These data clearly demonstrate the benefits of creating compressive residual stresses at the surface of a part by shot peening. In addition to improving the fatigue behavior of a part, controlled shot peening can also be used as a finishing process to generate three-dimensional surfaces such as those on aircraft wings and empennage skin. Additional examples of shot peening applications are listed in Ref 43. This process is described in detail in the article "Shot Peening" in this Volume.

Table 2 Fatigue life performance obtained by parts finished using various methods